Human spinal disc prosthesis

ABSTRACT

The invention relates to a spinal disc endoprosthesis. The endoprosthesis has a resilient body formed of one or more materials which may vary in stiffness from a relatively stiff exterior annular gasket portion to a relatively supple central nucleus portion. Concaval-convex elements at least partly surround that nucleus portion so as to retain the nucleus portion and gasket between adjacent vertebral bodies in a patient&#39;s spine. Assemblies of endoprosthetic discs, endoprosthetic vertebral bodies, and endoprosthetic longitudinal ligaments may be constructed. To implant this endoprosthesis assembly, information is obtained regarding the size, shape, and nature of a patient&#39;s damaged spine. Thereafter, one or more prosthetic vertebral bodies and disc units are constructed in conformity with that information. Finally, the completed and conformed vertebral body and disc assembly is implanted in the patient&#39;s spine.

This application and U.S. Ser. No. 10/713,837 are reissue applicationsof U.S. Pat. No. 5,865,846, which is a divisional of U.S. patentapplication Ser. No. 08/681,230, filed Jul. 22, 1996, U.S. Pat. No.5,674,296, and which is a continuation-in-part of U.S. patentapplication Ser. No. 08/339,490, filed Nov. 14, 1994, which isabandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to human prostheses, and especially tospinal column vertebral disc prostheses. The invention also relates tosurgical procedures for preparing the patient to receive a vertebraldisc endoprosthesis, and for implanting that endoprosthesis in thepatient's spine.

The herniation of a spinal disc and the often resultant symptoms ofintractable pain, weakness, sensory loss, incontinence and progressivearthritis are among the most common of debilitating processes affectingmankind. If a patient's condition does not improve after conservativetreatment, and if clear physical evidence of nerve root or spinal cordcompression is apparent, and if correlating radiographic studies (i.e.,MRI or CT imaging or myelography) confirm the condition, surgicalremoval of the herniated disc may be indicated. The process ofdiscectomy—as the name implies—involves the simple removal of the discwithout attempt to replace or repair the malfunctioning unit. In theUnited States in 1985, over 250,000 such operations were performed inthe lumbar spine and in the cervical spine.

Statistics suggest that present surgical techniques are likely to resultin short-term relief, but will not prevent the progressive deteriorationof the patient's condition in the long run. Through better pre-operativeprocedures and diagnostic studies, long-term patient results haveimproved somewhat. But it has become clear that unless the removed discis replaced or the spine is otherwise properly supported, furtherdegeneration of the patient's condition will almost certainly occur.

In the mid-1950's and 60's, Cloward and Smith & Robinson popularizedanterior surgical approaches to the cervical spine for the treatment ofcervical degenerative disc disease and related disorders of thevertebrae, spinal cord and nerve root; these surgeries involved discremoval followed by interbody fusion with a bone graft. It was noted byRobinson (Robinson, R.A.: The Results of Anterior Interbody Fusion ofthe Cervical Spine, J. Bone Joint Surg., 440A: 1569-1586, 1962) thatafter surgical fusion, osteophyte (bone spur) reabsorption at the fusedsegment might take place. However, it has become increasingly apparentthat unfused vertebral segments at the levels above and below the fusedsegment degenerate at accelerated rates as a direct result of thisfusion. This has led some surgeons to perform discectomy alone, withoutfusion, by a posterior approach in the neck of some patients. However,as has occurred in surgeries involving the lower back where discectomywithout fusion is more common as the initial treatment for discherniation syndromes, progressive degeneration at the level of discexcision is the rule rather than the exception. Premature degenerativedisc disease at the level above and below the excised disc can and doesoccur.

Spine surgery occasionally involves fusion of the spine segments. Inaddition to the problems created by disc herniation, traumatic,malignant, infectious and degenerative syndromes of the spine can betreated by fusion. Other procedures can include bone grafts and heavyduty metallic rods, hooks, plates and screws being appended to thepatient's anatomy; often they are rigidly and internally fixed. Noneprovide for a patient's return to near-normal functioning. Though theseprocedures may solve a short-term problem, they can cause other, longerterm, problems.

A number of attempts have been made to solve some of the problemsdescribed above by providing a patient with spinal disc prostheses, orartificial discs of one sort or another. For example, Steffee, U.S. Pat.No. 5,031,437, describes a spinal disc prosthesis having upper and lowerrigid flat plates and a flat elastomeric core sandwiched between theplates. Frey et al., U.S. Pat. Nos. 4,917,704 and 4,955,908, discloseintervertebral prostheses, but the prostheses are described as solidbodies.

U.S. Pat. Nos. 4,911,718 and 5,171,281 disclose resilient disc spacers,but no inter-connective or containing planes or like elements aresuggested, and sealing the entire unit is not taught.

It is the primary aim of the present invention to provide a vertebraldisc endoprosthesis which will perform effectively and efficientlywithin a patient's spine over a long period of time, and which will notencourage degeneration of or cause damage to adjacent natural discparts.

It is another object to provide a vertebral disc endoprosthesis whichdoes not require pins or other common mechanical hinge elements, yetwhich permits natural motion of the prosthetic parts and the adjacentnatural anatomy.

It is a related objective to provide a new vertebral disc endoprosthesissurgical procedure which will decrease post-operative recovery time andinhibit post-operative disc, vertebral body and spinal jointdegeneration.

It is yet another object to provide a method of installing theendoprosthesis so as to accurately mate the endoprosthesis with anadjacent specifically formed bone surface. An associated object is toprovide an endoprosthesis which will encourage bone attachment to, andgrowth upon, adjacent outer surfaces of the endoprosthesis.

Yet another object is to provide a vertebral endoprosthesis in which theparts are non-oncogenic.

Still another object is to provide a vertebral disc endoprosthesishaving a resilient element to accommodate shocks and other forcesapplied to the spine.

Another object is to provide a highly effective vertebral endoprosthesiswhich includes several disc endoprostheses and one or more prostheticvertebral bodies. A related object is to provide these elements in apre-assembled array for implantation in a patient.

SUMMARY OF THE INVENTION

To accomplish these objects, the invention comprises a resilient bodyformed of a material varying in stiffness from a relatively stiffexterior portion to a relatively supple central portion. Aconcaval-convex means at least partly surrounds that resilient body soas to retain the resilient body between adjacent vertebral bodies of apatient's spine. If medical considerations so indicate, several discendoprostheses can be combined with one or more endoprosthetic vertebralbodies in an entire assembly.

To implant this endoprosthesis assembly, information is obtainedregarding the size, shape, and nature of a patient's damaged naturalspinal discs. If one or more of the patient's vertebral bodies alsorequire replacement, information about those bodies is also obtained.Thereafter, one or more prosthetic disc units and interposed prostheticvertebral body units are constructed and preassembled in conformity withthat information. Finally, the completed and conformed prosthetic discand vertebral body assembly is implanted in the patient's spine.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings. Throughout the drawings, like reference numerals refer to likeparts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary vertical view of a portion of a human spine inwhich is installed a novel vertebral disc endoprosthesis embodying thepresent invention;

FIG. 2 is a fragmentary side elevational view similar to FIG. 1 showingthe elements of a patient's spine and having a novel vertebral discendoprosthesis embodying the present invention installed therein;

FIG. 3 is a sectional view taken substantially in the plane of line 3-3in FIG. 1;

FIG. 4 is an exploded view of the novel vertebral disc endoprosthesis;

FIG. 5 is a vertical fragmentary view of a patient's spine similar toFIG. 1, but showing a series of novel disc endoprosthesis unitsinstalled in the spine and interconnected to one another;

FIG. 6 is a fragmentary sectional view of a patient's spine similar toFIG. 3 and taken along line 6-6 in FIG. 5, but showing a natural uppervertebral body, and upper endoprosthetic disc; an adjacentendoprosthetic vertebral body; a second or lower endoprosthetic disc;and a second or lower natural vertebral body;

FIG. 7 is a sectional view taken substantially in the plane of line 7-7of FIG. 6;

FIG. 8 is a fragmentary side elevational view of the assembly shown inFIG. 6; and

FIG. 9 is a fragment vertical view, similar to FIG. 1, of a portion of ahuman spine in which is installed a variant form of the novel vertebraldisc endoprosthesis the variant form having a prosthetic longitudinalligament;

FIG. 10 is a sectional view taken substantially in the plane of line10-10 in FIG. 9;

FIG. 11 is a top view of a retainer means for use with a vertebral discendoprosthesis;

FIG. 12 is a sectional view taken substantially in the plane of line12-12 of FIG. 11;

FIG. 13 is a side view of a vertebral disc endoprosthesis having agroove for receiving the retainer means; and

FIG. 14 is a cross-sectional view of the retainer means in use.

DETAILED DESCRIPTION

While the invention will be described in connection with a preferredembodiment and procedure, it will be understood that it is not intendedto limit the invention to this embodiment or procedure. On the contrary,it is intended to cover all alternatives, modifications, and equivalentsas may be included within the spirit and scope of the invention asdefined by the appended claims.

Turning more specifically to FIGS. 1-3, a portion of a human spine 10 isshown. The illustrated spine 10 has been subjected to a discectomysurgical process. To discourage degeneration of or damage to the naturalvertebral bodies 12 and 14 and their respective facet joints, inaccordance with the invention, a vertebral disc endoprosthesis 18 isaffixed between the adjacent natural vertebral bodies 12 and 14. Herethis vertebral disc endoprosthesis 18 comprises a resilient disc body 20having a relatively stiff annular gasket exterior portion 22 and arelatively supple nuclear central portion 24. The annular gasket 22 canbe formed from a suitable biocompatible elastomer of approximately 90durometer hardness and the nuclear central portion 24 can be formed froma softer biocompatible elastomeric polymer of approximately 30 durometerhardness.

Concaval-convex means 30 surround the resilient body 20 to retain theresilient body 20 between the adjacent natural vertebral bodies 12, 14in a patient's spine 10. To this end, as shown in FIG. 3, theconcaval-convex means 30 comprise two generally L-shaped supports 32 and34. The supports 32, 34 each have confronting first concaval-convex legs42, 44, each leg being of relatively constant cross-sectional thickness.Each leg 42, 44 has an outer convex surface 52, 54 for engaging theadjacent bone of the natural vertebral bodies 12, 14. Correspondinginner concave surfaces 62, 64 in confronting array retain the resilientbody 20 in its illustrated compressive force shock-absorbing position.These supports 32 and 34 can undergo principle movement away from oneanother, but only limited secondary translational, rotational anddistractional motion will occur. Each support 32, 34 has a second wingor leg 72, 74 extending generally perpendicularly to the first legs 42,44 respectively, and adapted for affixation to the adjacent bonestructure. To carry out aspects of the invention described below, thisaffixation is effectively accomplished by cannulated screw devices 82,84 which may be of a biodegradable type manufactured by Zimmer of Largo,Fla. Each device 82, 84 comprises a screw 92, 94; and a screw anchor102, 104 adapted to threadably receive the screw extends radially intoand seats within the bone structure 12, 14 as especially shown in FIG.3.

To discourage and prohibit migration of fluids between theendoprosthesis 18 and adjacent parts of the anatomy, a seal member 110is attached to the supports 32, 34 so as to surround the resilient body20 comprised of the gasket 22 and nucleus 24, in accordance with anotheraspect of the invention. Here, this seal member 110 comprises a flexiblesheet material having a multiplicity of pores. Preferably, the pores arefrom about 5 microns to about 60 microns in size. A flexible, strongpolymer sheet material from which this seal is formed can be aKevlar-like material, or it can be Goretex-like material, or otherappropriate biocompatible material, such as polyether, polyurethane, orpolycarbonate urethane membranes, can be used. Kevlar material isoffered by the E. I. DuPont de Nemours Company of Wilmington, Delawareand Goretex material is offered by the W. T. Gore Company of Flagstaffand Phoenix, Arizona. Known sealing material can be applied to theflexible sheet material so as to render the flexible sheet materialsubstantially impervious to the passage of any fluid. A watertight sealis perfected when the seal 110 is glued or otherwise affixed to the legs42, 44 and mediate portions of the legs 72, 74 as suggested in FIGS.1-3.

In an alternative embodiment, the watertight seal between theendoprosthesis 18 and adjacent parts of the anatomy can be provided bydeveloping a groove 402 completely encircling the periphery of each ofthe legs 42, 44. Only one of the grooves is shown in FIG. 13. In thisembodiment, the seal member 410 is provided with a beaded edge 412 foreach groove. Additionally, a retaining band 415 is provided for eachgroove to retain the seal member 410 in grooves 402. The retaining bands415 can be in the form of a biocompatible monofilament wire of, forexample, stainless steel or titanium, a synthetic polymer cable or abraided wire cable. As shown in FIG. 11, each retaining band is crimpedanteriorly by a crimping sleeve 420. Of course, more than one crimpingsleeve may be used, if necessary. Although one sealing arrangementconsisting of the groove, beaded edge and retaining band is shown inFIG. 14, it should be understood that the sealing arrangement on theconcaval-convex leg of the other support is identical in design andfunction.

In use, the seal member 410 is placed about the concaval-convex means30. The retaining bands 415 are then placed adjacent to the respectivegroove 402 and crimped anteriorly, thereby fitting the bands into thegrooves. Each beaded edge 412 prevents the slipping of the seal memberunderneath the retaining band. Thus, the retaining band, the groove andthe beaded edge all cooperate to provide a water-tight seal to preventthe migration of fluids between the endoprosthesis 18 and adjacent partsof the anatomy. Glue can also be used to affix the seal member to theconcaval-convex means 30 as a supplemental means for perfecting theseal.

In accordance with another aspect of the invention, the supports 32, 34are formed of a biocompatible metal which may contain chromium cobalt ortitanium. Surface roughening or titanium beading 112, 114 on theexterior surfaces 52, 54 of legs 42, 44 encourages positive bondingbetween the adjacent bone and the convex surfaces 52, 54.

As suggested in FIGS. 9 and 10, a prosthetic longitudinal ligament 250can be connected between the screws 92, 94 to limit motions betweenelements of the spine 10 in the area where the endoprosthesis 18 isimplanted. This strap 250 may be made of the Kevlar-like material or theGoretex-like material described above, or it may be made of any otherstrong biocompatible material.

In accordance with another aspect of the invention, multipleendoprosthetic disc units can be placed in series with a straddlinginterlock appendage providing stability and fixation as shown in FIG. 5.Entire portions of a patient's spine can be replaced by a series ofinterconnected endoprosthetic vertebral bodies and endoprosthetic discunits. FIGS. 6-8 show an upper natural vertebral body unit 312 to whichan upper endoprosthetic body 308 has been attached. A lower naturalvertebral body 314 has attached, at its upper end, an endoprostheticdisc unit 318. Between these endoprosthetic disc units 308 and 318 is anendoprosthetic vertebral body 320. As suggested by FIG. 7, theendoprosthetic vertebral body 320 need not be irregularly shaped incross sectional aspect; rather, manufacturing processes may suggest thatit have a circular cross-sectional shape. As show in FIGS. 6 and 8, thisendoprosthetic vertebral body 320 comprises a titanium element 321, towhich are attached the preformed upper and lower endoprostheticvertebral body upper and lower concaval-convex elements 322, 324. Eachconcaval-convex element 322, 324 is attached to the prosthetic vertebralbody 320, as shown in FIG. 7, by extending set screws 330 through thetitanium vertebral body 321 into a stem-like projection 331 extendingfrom each of the concaval-convex elements 322, 324. A hole 360 in thebody 320 accommodates the stem-like projections 331 of theconcaval-convex elements 322 and 324. The stem-like projection 331 ofthe concaval-convex elements 322 and 324 is used only in conjunctionwith a prosthetic vertebral body implant construction 320.

An ear 340 is affixed, as by weldments 341, to a leg 342 extending froma concaval-convex element 322 as illustrated in FIGS. 6 and 8. An anchor352 can be threaded into the endoprosthetic vertebral body 320, and ascrew 362 can be turned into the anchor 352 so as to rigidly assemblethe leg 342 to a leg 354 extending from the lower endoprosthetic discunit 318.

The upper disc endoprosthesis 308, the endoprosthetic vertebral body320, and the lower disc endoprosthesis 318 can all be assembled andinterconnected as a unit before implantation in a patient's body whenindicated.

As also suggested in FIG. 6, the annular corners 372, 374 of naturalvertebral bodies 312, 314 each can extend irregularly radially outwardlyof the adjacent disc endoprosthesis 308, 318. However, the comers 382B,384B of the prosthetic vertebral body 320 do not generally extendsignificantly outside those disc units 308, 318, thus discouragingvertebral body engagement with and consequent abrasion or other damageto adjacent portions of the patient's natural anatomy. Preferably theendoprosthetic vertebral body 320 is not exactly right cylindrical inshape, but is rather slightly biconical; that is, the endoprostheticvertebral body 320 has a waist 390 of minimum radius R at an axialmedial point as suggested in FIG. 6.

According to yet another aspect of the invention, novel surgicalprocedures permit effective and permanent installation of theendoprosthetic vertebral body 320 and associated parts. First, a surgeonor medical technician develops information about the size, shape andnature of a patient's damaged vertebral body or bodies from radiographs,CT and/or MRI scans, noting specifically the anterior-posterior andlateral dimensions of the end plate of each involved vertebral body andthe vertical height of the anterior aspect of each involved vertebraland/or proximate vertebral body and vertical height of the mid portionof involved and proximate relatively normal intervertebral disc spaces.This information is transmitted by telephone, computer datalink ordocumentary transport to a specialized laboratory. That laboratoryconstructs one or more prosthetic assemblies of the sort shown in FIG. 6in conformity with the received information and this disclosure. Each ofthe assemblies can include a prosthetic vertebral body 321, and at eachbody end is a prosthetic disc 308,318. Each prosthetic disc unitcomprises, in turn, the concaval-convex elements 30; the resilient body20 interposed between the concaval-convex elements; and the seal unit110 secured around the interior legs and resilient body. Thereafter, thecompleted and conformed assembly is implanted in the patient's spine 10.

When the unit or units have been received and the patient properlyprepared, the damaged natural spinal disc or discs and vertebral body orbodies are removed and the adjacent spinal bone surfaces are milled orotherwise formed to provide concave surfaces to receive the confrontingconvex surfaces 52, 54. Thereafter, the disc units and vertebral bodyare installed in the patient's spine.

To accurately locate the concaval-convex surfaces in the patient'sspine, holes 382A, 384A (FIG. 3) are precisely located and then formedin the bone structure using a measuring instrument centered in theevacuated natural intravertebral disc space. These holes are then tappedto form female threads therein. When the threads have been formed, theanchors 102, 104 are implanted in the respective tapped holes, therebycreating reference points located precisely with respect to thepatient's spine. After the holes have been formed and the anchors 102,104 implanted, a bone surface milling jig (not shown) is affixed to theanchors 102, 104 and the desired concave surfaces of predetermined shapeare formed on the inferior and superior surfaces of the opposingvertebral bodies using one of a selection of predetermined milling heador bit sizes. Thereafter, the bone milling jig is removed and theconcaval-convex elements 52, 54 identical in shape to the milledsurfaces 112, 114 are inserted between the distracted milled vertebralbodies 12, 14. The distraction device is then moved. The concaval-convexconvex structures are then attached by the same anchors 102, 104 to thebone, thus insuring a precise and stable mate between the bone surfacesand the convex surfaces 52, 54.

If necessary, a damaged implanted nucleus and/or gasket 24 can beremoved and replaced. This can be accomplished by slitting the seal 110;removing the annular gasket 24 and damaged nucleus 22, and replacingthem with new, undamaged elements. Thereafter, the seal 110 can bere-established by suturing or gluing closed the slit seal.

1. A method of endoprosthetic discectomy surgery comprising the steps ofreceiving information about the size, shape and nature of a patient'sdamaged natural spinal vertebral bodies and discs from radiographs, CTand/or MRI scans or other imaging devices specifically determining theanterior-posterior and lateral dimensions of each involved vertebralbody, the vertical height of the anterior aspect of each involvedvertebral and/or proximate vertebral body, and the vertical height ofthe mid-portion of the involved and proximate normal intervertebral discspaces, thereafter constructing one or more prosthetic vertebral bodyunits and prosthetic disc units in conformity with the receivedinformation, each prosthetic disc unit including confronting L-shapedconcaval-convex elements and a resilient body interposed between theconcaval-convex elements; and an endoprosthetic vertebral bodyinterposed between and engaging the adjacent disc units; and thereafterimplanting the completed and conformed construction in the patient'sspine.
 2. A method according to claim 1 including the step ofconstructing a plurality of prosthetic disc units and further includingthe step of attaching the disc units to an endoprosthetic vertebral bodyprior to the step of supplying the assembly to the surgeon.
 3. A methodaccording to claim 1 further including the steps of surgically millingspinal bone surfaces with concave surfaces to receive confronting convexsurfaces of the concaval-convex elements, and installing at least onedisc unit having concaval-convex elements with said convex surfaces inthe patient's spine.
 4. A method of surgery comprising the steps ofremoving a vertebral disc from a patient's spine, forming holes atprecisely predetermined locations in bone structure adjacent thelocation of the removed disc, tapping the holes to form a female threadin each hole, and threadably implanting an anchor into each tapped hole,thereby creating reference points located precisely with respect to thepatient's spine, forming concave surfaces in adjacent spinal bone, andinserting between the formed bone surfaces a vertebral discendoprosthesis including confronting concaval-convex supports, eachsupport having an exterior convex surface adapted to mate with theadjacent formed concave spinal bone surface, the endoprosthesis furtherincluding a resilient body element interposed between theconcaval-convex supports, and thereafter affixing the concaval-convexsupports to the adjacent bone.
 5. A method of surgery according to claim4 further including the step of temporarily locating a bone surfacemilling jig at the site of the removed vertebral disc by means of saidanchors prior to implanting said disc endoprosthesis.
 6. A method ofsurgery according to claim 4 further including the steps of attaching ascrew to each concaval-convex support and screwing said screw into theimplanted anchor.
 7. A method of surgery according to claim 4 furthercomprising the steps of identifying a damaged resilient nucleus bodyelement or annular gasket in an implanted endoprosthesis, removing saiddamaged nucleus body element or annular gasket from the endoprosthesisand inserting a new, undamaged nucleus body element or annular gasketinto the endoprosthesis without removing the concaval-convex supportsfrom the patient's spine.
 8. A method of spinal surgery comprising thesteps of forming mounting holes in one or more vertebral bodies of apatient's spine; utilizing said mounting holes to mount a bone mill on apatient's spine; milling confronting bone surfaces on and in thepatient's spine to a predetermined surface shape; removing said mill;and thereafter mounting a vertebral disc endoprosthesis having apredetermined outer surface shape by means of the original mountingholes so that outer surfaces of the vertebral disc endoprosthesis mateprecisely with the previously milled bone surfaces.
 9. A method ofendoprosthetic discectomy surgery comprising the steps of receivinginformation about the size, shape and nature of a patient's involved andproximate normal natural spinal vertebral bodies and natural spinalvertebral discs from known imaging devices, thereafter constructing atleast one vertebral disc endoprosthesis comprising a resilient disc bodyand concaval-convex elements at least partly surrounding the resilientdisc body, removing at least the involved, natural spinal discs from thepatient's spine, forming concave surfaces in adjacent spinal bone, andthereafter implanting the vertebral disc endoprosthesis in the patient'sspine.
 10. A method of surgery comprising: implanting at least oneanchor into a hole having a predetermined position in an anteriorsurface of at least one vertebral body; affixing a bone surface millingmechanism to the at least one anchor; forming partially hemisphericalsurfaces in endplates of confronting vertebral bodies using the bonesurface milling mechanism; inserting between the formed partiallyhemispherical surfaces an intervertebral disc endoprosthesis,comprising: confronting concaval-convex supports, each support having anexterior convex surface adapted to mate with one of the formed partiallyhemispherical surfaces, and a resilient body interposed between theconcaval-convex supports such that the supports are capable of movementrelative to the resilient body element after the endoprosthesis has beeninserted between the formed partially hemispherical surfaces.
 11. Themethod of surgery according to claim 10, further comprising: removingthe bone surface milling mechanism after forming the partiallyhemispherical surfaces in the endplates of the vertebral bodies.
 12. Amethod of surgery comprising: forming concave surfaces in endplates ofconfronting vertebral bodies; and inserting between the formed concavesurfaces an intervertebral disc endoprosthesis wherein theintervertebral disc endoprosthesis comprises: L-shaped supports whereineach of the L-shaped support comprises an exterior convex surfaceadapted to mate with one of the formed concave surfaces; and a resilientbody interposed between the L-shaped supports.
 13. The method of claim12, further comprising affixing the L-shaped supports to the confrontingvertebral bodies.
 14. The method of claim 12, further comprisingimplanting at least one anchor in at least one of the confrontingvertebral bodies.
 15. The method of claim 14, wherein the implanting islocated in an anterior surface of the at least one of the confrontingvertebral bodies.
 16. The method of claim 15, further comprisingaffixing a bone surface milling mechanism to the at least one anchor.17. The method of claim 12, wherein the resilient body comprises arelative stiff portion and a relative supple portion.
 18. A method ofendoprosthetic discectomy surgery comprising: receiving informationabout a size, shape, and nature of a patient's involved natural spinalvertebral bodies and natural spinal vertebral discs from an imagingdevice; removing at least the involved and damaged natural spinal discmaterial from the patient's spine; implanting at least one anchor into ahole having a predetermined position in an anterior surface of at leastone adjacent vertebral body; forming concave surfaces in the adjacentvertebral bodies; and implanting into the patient's spine, anintervertebral disc endoprosthesis comprising a resilient disc body andconcaval-convex elements that at least partly surround and are capableof movement relative to the resilient disc body in the patient's spine.19. The method of claim 18, further comprising affixing a bone surfacemilling mechanism to the at least one anchor.
 20. The method of claim 18wherein the concaval-convex elements are adjacent to the resilient body.21. The method of claim 18 wherein the concaval-convex elements are incontact with the resilient body.